Too much GPU Core Voltage (mv)?

[TheQuestionS]

How do I overclock my Core Voltage (mv) in MSI afterburner? I see all these videos with it overclcoked yet mine is shaded out, and I can't move the bar.

Also, how much is too much Core Voltage? For example: 10? 50? 80?

 

[TheQuestionS]

Found the first part under MSI AB, General Tabs, Unlock Voltage : D Glad that parts over, but the voltage is one thing I have no clue about. CPU's I can work with, but not quite yet GPU volts. If It'll help I have a Gigabyte Geforce GTX 970 Windforce